Method of withdrawing the strand from a continuous casting machine



March 12, 1968 H. PAUELS ETAL METHOD OF WITHDRAWING THE STRAND FROM A CONTINUOUS CASTING MACHINE Filed Aug. 50, 1965 FIGZ DOC)

FIG-4 FIGB . IggVENTgRS ATTORNEYS United States Patent Office 3,372,?31 Patented Mar. 12, 1968 3,372,731 METHOD OF WITHDRAWING THE STRAND FROM A CONTINUUUS CASTING MACHINE Heinrich Panels, Dusseldorf-Lohausen, Germany, and Walter Meier, Winterthur, Switzerland, assignors to Schloemann Ahtiengeselischaft, Dusseldorf, Germany, and Concast A.G., Zurich, Switzerland Filed Aug. 30, 1965, Ser. No. 483,525 Claims priority, application Germany, Aug. 29, 1964, Sch 35,703 5 Claims. (Cl. 164-82) ABSTRACT OF THE DISCLOSURE During withdrawal of the dummy bar head and the strand attached thereto from a continuous casting mold, an abrupt dimensional discontinuity interrupts smooth withdrawal when the discontinuity enters a withdrawal roll. To prevent this, the applicant reduces the abrupt discontinuity by shaping of the dummy bar head and allowing the discontinuity to enter a smoothing roller in such manner as to make the transition from head to strand smooth.

This invention relates to a method of withdrawing the strand from a continuous casting machine, in which liquid metal is poured into a cooled mould whose exit end is closed by a dummy bar and the strand is withdrawn from the mould by the dummy bar engaged by withdrawing rolls, and an apparatus for performing the method. The invention is advantageously applied to the casting of slabs.

When continuous casting machines are started up, the mould is closed by a dummy bar whose bottom end is in the range of operation of a set of withdrawing rolls. To ensure that the dummy bar head does not jam in the cross sectional zone of the mould and scrape the mould wall, its cross section must be made smaller than the free cross section of the mould.

The resultant gap between the mould wall and the dummy bar head will vary with the size of the strand and may the as much as mm. and is closed by a sealant to prevent any passage of liquid material. To prevent any fusion between the beginning of the strand and the dummy bar head, the latter is covered by an asbestos sheet. To enable the cast strand in the mould to be withdrawn by means of the dummy bar, the dummy bar head is formed with recesses to receive bars or rails which connect the solidified strand with the dummy bar.

The smaller cross section of the dummy bar head as compared with the cross section of the mould cavity means that there is an abrupt change of cross section between the casting and the dummy bar head and this results in scams or joints. These are very unfavorable as regards introduction of the strand into the withdrawing rolls because they obstruct such introduction or catch against the withdrawing rolls and make introduction impossible. Conditions are very unfavorable in continuous casting machines in which the strand is guided in an arcuate guiding system after the mould, since the shape of the arc causes the dummy bar head to bear unilaterally against the mould wall so as to form a unilateral seam. The difference between strand and dummy bar head thickness on this unilateral seam prevents the strand from being engaged by withdrawing rolls. Also, the straightening process carried out in the combined withdrawing and straightening unit usually used in arcuate machines of this kind causes a bending force to be exerted on the dummy bar head and this is transmitted to the connecting elements between the dummy bar head and the strand. The increased traction due to the seam and the bending force usually cause the connecting elements to break or at least cause the withdrawing rolls to slip. Such slip is increased by the fact that there is a shrinkage gap between the dummy bar head and the beginning of the strand and this gap is further increased by the asbestos sheet. These disadvantages usually result in interrupted casting.

It is, therefore, an object of the present invention to obviate the above described economic drawbacks by reducing the effect of different strand and dummy bar head thickness on the withdrawing rolls, thus, ensuring reliable engagement of the strand by said rolls.

Thus, according to the present invention, the effective difference between strand and dummy bar head thickness on the seam forming during casting at the connection between the dummy bar head and the beginning of the strand is reduced for entry into the withdrawing rolls. This reduction of the difference of thickness can be obtained by the provision of a pair of rolls upstream of the withdrawing rolls. The rolls operative on the seam or joint side will be adjustable perpendicular to the axis of the strand, the amount of adjustment varying during entry of the seam and the effective difference between strand and dummy bar head thickness being rolled away. This difference in thickmess on the seam may alternatively be reduced by blades disposed upstream of the withdrawing rolls.

Another solution is to reduce the effective difference between strand and dummy bar head thickness on the seam by flame de-seaming before the seam enters the withdrawing rolls. Such flame de-seaming may be carried out manually or automatically by a flame de-seaming machine in which latter case, the machine moves in synchronism with the speed of extraction of the strand during the machine operation.

Advantageously, the beginning of the strand is produced with an end face differing from the direction of the lines of attack of rolls and the effective difference between strand and dummy bar head thickness is rolled to be wedge-shaped. By producing the strand with an end face differing from the direction of the lines of attack of rolls, for example, with an end face extending at an angle to the strand axis, only part of the beginning of the strand initially comes into the range of operation of the rolls preceding the withdrawing rolls and is rolled away so as to be wedge-shaped. This entry by a partial zone enables control of the adjustment during rolling to be dispensed with.

In another solution, the effective difference between strand and dummy bar head thickness on the seam on entry into the withdrawing rolls is rolled to be wedgeshaped by the contact pressure required for extraction of the strand. The preferable V-shaped end face initially passes \by just its tip into the withdrawing rolls. The very high specific pressure on this tip as a result of the withdrawing roll contact pressure results in direct wedgeshaped rolling away of this tip so that the next zone of the end face is reliably drawn into the withdrawing rolls. The withdrawing rolls contact pressure is additionally increased by the wedge effect and this reduces any risk of slipping off the withdrawing rolls.

The apparatus required for performing the method for producing an end face differing from the direction of the line of attack of the roll is characterised in that the dummy bar head end face facing the beginning of the strand is V-shaped or extends at an angle to the strand axis.

Having briefly described this invention, it will be described in greater detail in the following portions of the specification, which may best be understood by reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic view of a continuous casting machine with an arcuate strand guiding system and an additional pair of rolls;

FIG. 2 shows the connection between the dummy bar and the strand with a unilateral seam, or joint in accordance with the present invention;

FIG. 3 shows a dummy bar head with a V-shaped end face according to the present invention; and

FIG. 4 shows a dummy bar head with an inclined end face according to the present invention.

FIG. 1 illustrates a ladle 1, from which the liquid metal flows to a tundish 2. From the latter, the metal is poured into a water-cooled mould 3. In this example, the mould 3 is of arcuate shape to form a curved strand. Before the steel is poured, the extraction end of the mould I3 is closed by a dummy bar 4 (FIG. 2) or by the dummy lbar head 5. The cross section of the dummy head 5 is a few millimeters smaller than the cross section of the cavity of the mould 3, as already indicated hereinbefore. The dummy bar 4 extends from the mould 3 to a withdrawing and straightening unit 6, the first pair of withdrawing rolls of which bears the reference 7. As soon as the liquid metal poured into the mould 3 has formed a solidified shell, the resultant strand 8 with a liquid core is withdrawn from the mould by the dummy bar 4 driven by the unit 6 and is guided in a curved guide having a secondary cooling system 16, in which it is cooled still further.

Since the dummy bar head 5 bears against the outside curve of the mould 3 unilaterally, there is an abrupt unilateral change of cross section in the form of a seam or joint 9 (FIG. 2). As already stated, the effect of the seam 9 on the drive rolls 7 is increased by the shrinkage of the solidifying metal and by the gap due to the asbestos sheet disposed on the dummy bar head.

FIG. 3 shows a dummy bar head 5 to an enlarged scale. The dummy bar 4 is in the form of a chain so that it can follow the curved guide 15. I-rails are incorporated in the head 5 and acts as connecting elements between the dummy bar head and the solidified strand and transmit the extracting force from the dummy bar 4 to the cast strand 8. The direction of the end face 21 deviates from the direction of lines of attack of the withdrawing rolls 7 and is shaped to extend in the form of a V in relation to the strand axis.

FIG. 4 shows another construction of the end face 22. It again has a direction different from the direction of lines of attack of the withdrawing rolls 7 and extends at an angle to the strand axis.

When the strands being cost have dummy bar head end faces extending perpendicularly to the strand axis, the unit 6 may be preceded by a roll stand 25 with an adjustable top roll. As soon as the seam 9 reaches the zone of the rolls 25, the top roll 25 is adjusted to roll away the effective difference between strand and dummy bar head thickness on the seam 9 by forming a wedge shape so that the strand can be reliably introduced into the following roll stand of the roll 7.

If, however, the strand being cast has a V-shaped end face, the additional roll stand 25 can be eliminated, since the contact pressure of the withdrawing rolls 7, which may be as much as 100 metric tons for large strand cross sections, is sufficient to roll part of the incoming tip of the V-shaped end face of the hot strand to give it a wedge-shape. This rolled zone is suflicient to prevent the strand or its seam 9 from catching on the withdrawing rolls 7 so that the latter slips.

According to FIGS. 3 and 4, the end faces differing from the direction of the lines of attack of the rolls 25 or rolls 7 are in the form of plane surfaces, but the invention covers other shapes. For example, they may be arcuate.

This invention may be variously modified and embodied within the scope of the subjoined claims.

What is claimed is:

1. In withdrawing a strand in a continuous casting machine, in which liquid metal is poured into a cooled mould, the exit end of said mould being initiallv closed partly by a dummy bar of smaller dimension than the exit end of said mould whereby the transverse cross section of the casting is larger than that of the dummy bar with :an abrupt dimensional discontinuity at the connection, said strand issuing from said mould and being connected with said dummy bar as said dummy bar is engaged by and withdrawn from said mould by withdrawal rolls, said strand being guided by strand guiding means positioned between said mould and said withdrawal rolls and cooled further by cooling means positioned between said mould and said withdrawal rolls, the improvement which comprises making the end of the casting with a sloping face at its connection with the dummy bar across at least the part of the casting which extends beyond the cross section of the dummy bar, the slope being at an acute angle to a transverse plane normal to the direction of movement of the casting through a pass between said withdrawal rolls to prevent interruption of smooth withdrawal by the entry of the discontinuity into the withdrawal roll pass.

2. The method in accordance with claim 1 in which the reduction of the abruptness of the dimensional discontinuity includes the step of making the sloping face by rolling down the discontinuity at a location between the mould and the withdrawal rolls to produce a wedge shape for entry into the pass between the withdrawal rolls.

3. The method in accordance with claim 1 which includes the step of making the connection between the strand and the dummy head in a V-shape.

4. The method in accordance with claim 1 which includes the step of making the connection between the strand and the dummy head at an angle to a plane normal to the longitudinal axis of said strand.

5. The method in accordance with claim 1 which includes sloping the end of the casting to reduce the abruptness of said discontinuity, by flaming.

References Cited UNITED STATES PATENTS 379,096 3/1888 Brooke 164337 X 425,846 4/1890 Atha 164263 494,659 4/1893 Very 164283 X 2,176,990 10/1939 Crampton 164274 3,262,161 7/1966 Andrzejak et al 164274 3,266,104 8/1966 Feldessy et a1 164274 2,283,368 11/1966 Heman 164-282 FOREIGN PATENTS 901,091 10/ 1944 France.

674,136 4/ 1939 Germany.

840,676 7/1960 Great Britain.

1. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner. 

